1. Field of the Invention
The present invention relates to a piezoelectric vibrating reed, a piezoelectric vibrator, a method of manufacturing a piezoelectric vibrator, an oscillator, an electronic apparatus, and a radio-controlled timepiece.
2. Description of the Related Art
In recent years, piezoelectric vibrators using crystal or the like are used in mobile phones or portable information terminals as a time source, a control signal timing source, a reference signal source, and the like. Various piezoelectric vibrators are available as such kinds of piezoelectric vibrators. For example, a piezoelectric vibrator in which a so-called tuning fork type piezoelectric vibrating reed is sealed in a package or a piezoelectric vibrator in which a so-called AT cut type piezoelectric vibrating reed is sealed in a package is known.
For example, as disclosed in JP-A-2001-144581, a tuning fork type piezoelectric vibrating reed is formed by a thin plate shaped crystal piece in which two arms (equivalent to vibrating portions in this application) extend from a base portion. Moreover, a pair of excitation electrodes is formed at a predetermined distance therebetween on each of the upper and lower surfaces of each arm of the piezoelectric vibrating reed. In addition, a pair of mount electrodes is formed on each of the upper and lower surfaces of the base portion, and is electrically connected to the pair of excitation electrodes through a pair of lead-out electrodes.
The excitation electrodes and the lead-out electrodes are formed by single films made of chromium, for example, and are covered by an insulating film (equivalent to a passivation film in this application) for preventing short-circuiting. On the other hand, an electrode film for the mount electrodes is formed by a laminated film of chromium (Cr) and gold (Au), for example. Here, the mount electrodes are exposed from the passivation film.
Then, the mount electrodes of the piezoelectric vibrating reed are mounted on internal electrodes of a package. Thus, a piezoelectric vibrator is formed. As a method of mounting a piezoelectric vibrating reed, a method is effective in which a piezoelectric vibrating reed is picked up using a bonding head of a flip chip bonder and then mount electrodes of the picked piezoelectric vibrating reed are pressed against bumps on internal electrodes and the bonding head is made to vibrate ultrasonically so that the mount electrodes and the bumps are ultrasonically bonded to each other.
However, if the bonding head comes in contact with the mount electrode exposed from the upper surface of the base portion while the bonding head is vibrating ultrasonically, there is a possibility that an electrode material, such as gold, on the mount electrode surface, will adhere to the bonding head. Moreover, if a piezoelectric vibrating reed to be mounted next is picked up by the bonding head in a state where an electrode material adheres to the bonding head, the electrode material enters between the bonding head and the piezoelectric vibrating reed to be mounted next. Even if ultrasonic bonding is performed in this state, the bonding head cannot apply ultrasonic vibration to the piezoelectric vibrating reed. As a result, the mount electrode and the bump may not be ultrasonically bonded to each other. Moreover, since the electrode material enters between the piezoelectric vibrating reed and the bonding head even if the mount electrode and the bump could be ultrasonically bonded, the piezoelectric vibrating reed may be bonded in an inclined state. Then, interference with a package may occur when the piezoelectric vibrating reed bonded in the inclined state vibrates. As a result, manufacturing failure, such as a situation where the piezoelectric vibrating reed cannot be made to vibrate at a predetermined frequency, may occur.
In addition, it is also possible to set a head cleaning step of moving a bonding head and wiping an electrode material adhering to the bonding head by rubbing using a cleaning pad, for example, after a predetermined number (for example, about 10 to 20 times) of piezoelectric vibrating reed mounting steps have ended. However, when the head cleaning step is set, the number of steps in manufacturing a piezoelectric vibrator increases.